JP2000283741A - Fringe detector, photosensitive drum tester using the same, liquid crystal tester using the same, fringe detecting method, and medium with recorded fringe detection program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stripe detector which can compute the characteristic quantity of fringe including a direction of fringe. SOLUTION: This fringe detector is provided with a square block dividing part 21 to dividing an optical fringe picture of a photographed object to be tested into blocks comprising a plurality of assembled picture elements, a DCT processing part 22 to convert through discrete cosine an information within the blocks divided by the square block dividing part 21, a fringe candidate block extraction part 24 to extract a fringe candidate block every conversion coefficient on the basis of the processing result by the DCT processing part 22, and a directional filter processing part 25 to apply a filter for processing in consideration of directionally to the fringe candidate block extracted every conversion coefficient by the fringe candidate block extraction part 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for detecting and evaluating optical fringes such as interference fringes and moiré fringes appearing on the surface of an inspection object, and more particularly to a fringe feature quantity including the direction of optical fringes. The present invention relates to a fringe detecting device for calculating the surface condition of an inspection object by calculating the following, a photosensitive drum inspecting device using the same, a liquid crystal panel inspecting device using the same, a fringe detecting method, and a medium recording a fringe detecting program.

[0002]

2. Description of the Related Art In recent years, with the mass production of products, various techniques for automatically inspecting an inspection object have been developed. One of the techniques is optically generated depending on the surface state of the inspection object. There is a technique for detecting a defective portion of an inspection object by imaging a stripe to be inspected and analyzing the stripe. Japanese Unexamined Patent Publication No. Hei 7-260457,
JP-A-9-61125 and JP-A-10-132
There is an invention disclosed in JP-A-535-535.

A surface inspection apparatus disclosed in Japanese Patent Application Laid-Open No. Hei 7-260457 discloses an image pickup unit for picking up an interference fringe pattern image of a surface to be inspected, and an A / D converter for obtaining image data based on a video signal from the image pickup unit. And an interference fringe state detecting unit for detecting an arrangement state of an interference fringe forming an interference fringe pattern image represented by each unit section corresponding to a predetermined unit period in the image data obtained by the A / D conversion unit And a defect detection unit that detects a change in interference fringes due to a defect on the surface to be inspected based on a detection output from the interference fringe state detection unit.

This surface inspection apparatus detects a defect on a surface to be inspected by utilizing the fact that interference fringes at a defective portion become dense. That is, the interference fringe state detection unit calculates the fringe interval (fringe cycle) for the captured image including the interference fringes based on the grayscale profile of each horizontal line.
Then, the defect detection unit determines whether the number of fringes in each of a predetermined range converted from the fringe period on the inspected surface or the portion where the fringe period on the inspected surface is smaller than the fringe period on the predetermined non-defective product is a predetermined number. A portion having more stripes than a good product is detected as a defective portion.

[0005] A laminated plate inspection system disclosed in Japanese Patent Application Laid-Open No. 9-61125 discloses a laser light source for irradiating an object to be inspected (a laminated plate obtained by laminating two flat glasses) with a laser light source. A TV camera that captures an interference fringe image of the inspection object that appears due to the irradiation of the light beam, and a CPU (Central Processing U) that determines an area where the fringe pitch of the interference fringe captured by the TV camera is denser than a predetermined value.
nit).

The CPU performs an FFT (fast Fourier transform) process on the interference fringe image picked up by the TV camera, performs a high-pass filter process so as to leave a portion having a frequency equal to or higher than a predetermined frequency, and then performs an inverse FFT process. . CP
U detects, from the image obtained by the inverse FFT processing, a portion left as a high frequency region as a defective portion.

Further, the surface inspection apparatus disclosed in Japanese Patent Laid-Open No. 10-132535 discloses a light projecting unit that divides a laser beam into two and irradiates the surface to be inspected, and receives light reflected from the surface to be inspected. It includes a light receiving unit, an image conversion unit that optically Fourier-transforms interference fringes formed on the surface to be inspected, and a display unit that displays an optical Fourier transform image formed by the image conversion unit. The presence or absence of a defect on the surface to be inspected is clarified by displaying the optical Fourier transform image formed by the image conversion unit on the display unit.

This surface inspection apparatus performs inspection by spot measurement by irradiating a surface to be inspected with laser light, and enables two-dimensional scanning with laser light to detect a defective portion in a wide area. .

[0009]

However, Japanese Patent Application Laid-Open No. Hei 7-2
In the surface inspection apparatus disclosed in Japanese Patent No. 60457,
Figure 1 shows that the period of the interference fringes can be measured accurately.
6A, the horizontal direction 103 of the captured image 102
This is the case where the stripe 101 is perpendicular to. That is, in this case, the actual period D of the interference fringes 101 matches the measured value d. However, when the interference fringes 101 are not perpendicular to the horizontal direction 103 of the captured image 102 as shown in FIG. 16B (the interference fringes 101 have an angle θ (θ <θ 90
°)), there is a problem that the period d of the interference fringes 101 calculated from the shading profile is larger (1 / sin θ times) than the period D of the actual interference fringes 101.

Also, as shown in FIG.
Is coincident with the horizontal direction 103 of the captured image 102, the characteristics of the interference fringes 101 do not appear in the shading profile, and the measurement of the period of the interference fringes 101 is practically impossible. The interference fringes 101 are shown in FIGS. 16 (a) to 16 (c).
It is extremely rare that a straight line is formed as shown in FIG.
The value of the angle θ of the interference fringe 101 with respect to 03 varies depending on the measurement position. Therefore, it is impossible to calculate the angle θ in line-by-line (fringe period) measurement, and it is impossible to accurately measure the period of the interference fringe 101 at an arbitrary position.

Further, in the laminated board inspection system disclosed in Japanese Patent Application Laid-Open No. 9-61125, it is effective for stripes generated entirely in the inspection area, but partially generated in the inspection area. FF that is not effective for stripes
There is a problem specific to T. That is, in the frequency distribution obtained by the FFT, the characteristics of the stripes partially generated in the inspection area do not appear so strongly, so that there is a problem that the sensitivity is weak and the detection of the stripes becomes difficult.

Further, even if a stripe generated partially in the inspection area can be detected, it can only be confirmed that the stripe exists in the inspection area, and it cannot be detected up to the position of the stripe. There were also problems. This problem is due to the fact that the Fourier transform is a signal transform based on a sine wave that is repeated infinitely. Therefore, it can be said that the FFT can be effectively used in the image signal processing when the frequency of the target image is known in advance and the purpose is to remove high-frequency noise that spreads over the entire inspection area.

A surface inspection apparatus disclosed in Japanese Patent Application Laid-Open No. Hei 10-132535 solves the above-mentioned problem of Fourier transform. That is, in this surface inspection apparatus, stripes are detected by performing an optical Fourier transform on an image in a minute range (laser spot diameter). By performing this processing while scanning two-dimensionally,
It enables a wide range of measurements. Therefore, it is possible to accurately determine the presence or absence of a fringe that spreads over a region having a size equal to or larger than the laser spot diameter. In addition, since the position of the stripe can be specified from the scanning position at that time, if the laser spot diameter is made sufficiently small, the portion where the stripe occurs can be detected with high sensitivity.

However, since the process is not a process taking into account the direction of the fringes and the two-dimensional continuity, images other than fringes appearing due to light interference, for example, white noise, unevenness in the reflectivity of the surface of the inspection object, or change in brightness due to texture, etc. When affected, there is a problem that these cannot be removed separately from interference fringes.

The present invention has been made to solve the above problems, and a first object of the present invention is to provide a fringe detecting device capable of calculating a fringe feature amount including a fringe direction. It is.

A second object of the present invention is to provide a fringe detecting apparatus capable of detecting fringes with high robustness, which is not affected by a change in fringe contrast due to a change in illumination intensity or a change in light reflectance on the surface of the inspection object. It is.

A third object is to provide a fringe detecting device capable of eliminating the influence of brightness change due to white noise, reflectance unevenness on the surface of an inspection object, or texture.

A fourth object of the present invention is to provide a photoreceptor drum inspection apparatus capable of calculating a fringe feature quantity including a direction of a fringe and accurately detecting a defective portion.

A fifth object of the present invention is to provide a liquid crystal panel inspection apparatus capable of calculating a fringe feature quantity including a direction of a fringe and accurately detecting a defective portion.

[0020]

According to a first aspect of the present invention, there is provided a fringe detecting apparatus, comprising: a dividing unit configured to divide a captured image of an optical fringe of an inspection object into blocks each including a plurality of pixel sets; Processing means for performing a discrete cosine transform on information in the block divided by the dividing means,
Evaluation means for evaluating the inspection object based on a processing result by the processing means.

The processing means performs a discrete cosine transform on the information in the block divided by the dividing means, so that it is possible to calculate the fringe feature quantity including the direction of the fringe.
The fringes can be accurately detected.

The fringe detecting device according to the second aspect is the first aspect.
In the fringe detecting device described above, the evaluating unit generates a two-dimensional matrix for each transform coefficient obtained by the processing unit, and extracts a block having a relatively large amplitude in the two-dimensional matrix as a fringe candidate block. Extraction means.

Since the extracting means extracts a block having a relatively large amplitude as a fringe candidate block in the two-dimensional matrix, the influence of a change in fringe contrast due to a change in illumination intensity or a change in light reflectance on the surface of the inspection object. Can be eliminated, and a highly robust fringe can be detected.

According to a third aspect of the present invention, there is provided a fringe detecting apparatus.
In the fringe detection device described above, the extraction unit includes a calculation unit for calculating an average value and a standard deviation for each conversion coefficient with respect to a processing result obtained by the processing unit, and the average value and the standard deviation calculated by the calculation unit. And a fringe candidate block extracting means for extracting a fringe candidate block based on

Since the fringe candidate block extracting means extracts fringe candidate blocks based on the average value and the standard deviation calculated by the calculating means, it is possible to detect fringes having higher robustness.

According to the fourth aspect of the present invention, there is provided a fringe detecting apparatus.
In the fringe detecting device described above, the fringe candidate block extracting means extracts a block in which a distance between a conversion coefficient and an average value of the block is equal to or larger than a value obtained by multiplying a standard deviation by a predetermined value as a fringe candidate block. Means.

Since a block in which the distance between the conversion coefficient of the block and the average value is equal to or larger than a value obtained by multiplying the standard deviation by a predetermined value is extracted as a fringe candidate block, the fringe candidate block can be easily extracted. become.

According to a fifth aspect of the present invention, there is provided a fringe detecting device.
In the fringe detecting device according to any one of the above (1) to (4), the evaluating means further extracts, from among the fringe candidate blocks extracted by the extracting means, blocks having similar fringe feature amounts and adjacent fringe candidate blocks. And a stripe extracting means.

The fringe extracting means extracts similar blocks from the fringe candidate blocks extracted by the extracting means, and extracts the blocks in which the fringe candidate blocks are adjacent to each other. Alternatively, it is possible to eliminate the influence of brightness change due to texture.

According to a sixth aspect of the present invention, there is provided a fringe detecting device.
In the fringe detecting device described above, the fringe extracting unit includes a filter processing unit for performing a filtering process in consideration of directionality on the fringe candidate block for each transform coefficient extracted by the extracting unit.

The filter processing means performs filter processing in consideration of directionality on the stripe candidate block for each transform coefficient extracted by the extraction means, so that it is possible to further eliminate the influence of a change in brightness.

According to a seventh aspect of the present invention, there is provided a fringe detecting apparatus according to the sixth aspect.
The fringe detecting device as described above, wherein the fringe detecting device further includes a merging unit for merging processing results for each conversion coefficient by the filter processing unit.

The merging means merges the processing results for each of the transform coefficients by the filter processing means, so that stripes in all directions can be output as processing results.

The fringe detecting device according to the eighth aspect is the first aspect.
8. The fringe detecting device according to any one of items 1 to 7, wherein the processing unit includes a unit for extracting only a specific transform coefficient from the transform coefficients obtained by the discrete cosine transform.

Since only a specific transform coefficient is extracted from the transform coefficients obtained by the discrete cosine transform, the processing can be speeded up.

According to a ninth aspect of the present invention, there is provided a photoreceptor drum inspection apparatus, wherein light emitting means for irradiating light to the photoreceptor drum and optical fringes of the photoreceptor drum generated by light reflected from the light emitting means are imaged. An imaging unit for controlling the rotation of the photosensitive drum, a dividing unit for dividing an image captured by the imaging unit into blocks each including a plurality of pixel sets, and a dividing unit. The processing unit includes a processing unit for performing a discrete cosine transform on information in the divided blocks, and an evaluation unit for evaluating the photosensitive drum based on a processing result by the processing unit.

The processing means performs a discrete cosine transform on the information in the block divided by the dividing means, so that it is possible to calculate the stripe characteristic amount including the direction of the stripe of the photosensitive drum. Inspection can be performed accurately.

According to a tenth aspect of the present invention, there is provided a liquid crystal panel inspection apparatus for irradiating a liquid crystal panel with light, and for imaging optical fringes of the liquid crystal panel generated by reflected light of the light from the light emitting means. An imaging unit; a dividing unit configured to divide an image captured by the imaging unit into blocks each including a plurality of pixel sets; and a unit configured to perform a discrete cosine transform on information in the blocks divided by the dividing unit. A processing unit; and an evaluation unit for evaluating the liquid crystal panel based on a processing result by the processing unit.

The processing means performs the discrete cosine transform on the information in the block divided by the dividing means, so that it is possible to calculate the fringe feature amount including the direction of the fringe of the liquid crystal panel. Can be performed accurately.

According to a eleventh aspect of the present invention, there is provided a fringe detecting method for dividing a captured image of an optical fringe of a test object into blocks each including a plurality of pixel sets, And performing a discrete cosine transform on the inspection object, and evaluating the inspection object based on a processing result of the discrete cosine transform.

Since the discrete cosine transform is performed on the information in the divided blocks, it is possible to calculate the fringe feature amount including the direction of the fringe, and to accurately detect the fringe.

According to a twelfth aspect of the present invention, a fringe detection program recorded on a medium divides a captured image of an optical fringe of an inspection object into blocks each including a plurality of pixel sets. Performing a discrete cosine transform on the information in the block; and evaluating the inspection object based on a processing result of the discrete cosine transform.

Since the discrete cosine transform is performed on the information in the divided blocks, it is possible to calculate the fringe feature amount including the direction of the fringe, and to accurately detect the fringe.

[0044]

(Embodiment 1) FIG. 1 is a block diagram showing a schematic configuration of a fringe detecting device according to Embodiment 1 of the present invention. This fringe detecting device includes a rectangular block dividing unit 21 that divides a captured image into rectangular blocks each including a plurality of pixel sets, a DCT processing unit 22 that performs DCT (discrete cosine transform) processing on the rectangular blocks,
An average value / standard deviation calculation unit 23 for calculating an average value and an average deviation for each conversion coefficient obtained by the T processing, and a fringe candidate based on the average value and the standard deviation calculated by the average value / standard deviation calculation unit 23 The directionality is determined with respect to a stripe candidate block extraction unit 24 that extracts a rectangular block that becomes a pattern, and a set of rectangular blocks that are stripe candidates extracted by the stripe candidate block extraction unit 24 (hereinafter, referred to as a stripe candidate block group). It includes a direction-specific filter processing unit 25 that performs the filtering process in consideration of the above, and a processing result merge unit 26 that superimposes the processing results obtained by the direction-specific filter processing unit 25.

FIG. 2 is a flowchart for explaining the processing procedure of the fringe detecting device according to the present embodiment. The processing procedure of this fringe detection device will be described with reference to other drawings as appropriate.

FIG. 3 schematically shows an image when an optical fringe such as an interference fringe generated depending on the surface condition of the inspection object is imaged. FIG. 3 illustrates a state in which the optical fringe 31 is captured in the entire captured image 32, and the resolution is 5%.
12 × 512 pixels (pixel MI = ｛I _ij ; 0 ≦ i, j ≦ 5
11｝). Note that the resolution of the captured image 32 may be another number of pixels, and the pixels 34 may not be square.

First, the rectangular block dividing unit 21 divides the captured image 32 into rectangular blocks each composed of a plurality of pixel sets (S1). FIG. 4 shows a state where the captured image 32 is subdivided into rectangular blocks 35. This rectangular block is converted into a square block of 8 × 8 pixels (MP = ｛P _xy ; 0 ≦
x, y ≦ 7}), the captured image 32
4 × 64 block matrix (MB = ｛MP _mn ; 0
≦ x, y ≦ 63}. The rectangular block MP may have a size other than this, and may not be a square.

Next, the DCT processing unit 22 performs the DCT processing for each rectangular block obtained by the rectangular block dividing unit 21.
Processing is performed to obtain a transform coefficient matrix composed of 8 × 8 (in the case of 8 × 8 pixels) transform coefficients (S2). The position coordinates of each pixel constituting the rectangular block MP are represented by (x,
y), the gray value of the pixel is P _xy ; 0 ≦ x, y ≦ 7, the conversion coefficient position in the conversion coefficient matrix MS is (u, v), and the conversion coefficient is S _uv ; 0 ≦ u, v ≦ 7. Then, the orthogonal transformation equation is as follows.

[0049]

(Equation 1)

FIG. 5 is a diagram showing a base image corresponding to the transform coefficient _Suv . The shading change of the base image becomes a COS waveform, but for convenience of illustration, the portion where the value of COS is positive is white,
It is assumed that a negative portion is represented by binary values as black. Further, each of the base images shown in FIG. 5 corresponds to the image at the (u, v) position of the 64 orthogonal base image matrices, and if the value of the transform coefficient S _uv is large, the base image at the (u, v) position This means that the components of the base image are strongly included.

As can be seen from FIG. 5, the base image contains many high-frequency horizontal frequency components (vertical stripes) as going from left to right, and contains many high-frequency vertical frequency components (horizontal stripes) as going from top to bottom. Thus, a rectangular block MP of 8 × 8 pixels is represented by a linear combination of the 64 base images. Therefore, by reading the distribution state of the S _uv value in the transform coefficient matrix MS, the stripe feature amount (direction, direction,
(Cycle, amplitude) can be easily grasped.

However, in general, white noise is likely to be included in the high-frequency region, and it is meaningless to treat the high-frequency region from the viewpoint of image resolution. Therefore, it is better to cut off the high-frequency component and focus on the relatively low-frequency region. It is valid. Therefore, of the 64 transform coefficients S _uv , 12 transform coefficients E = ｛(u, v) corresponding to the base image surrounded by the broken line in FIG.
= (0,2), (0,3), (0,4), (1,2),
(1,3), (1,1), (2,2), (2,1),
Only (3, 1), (2, 0), (3, 0), (4, 0)} will be selected as stripe evaluation targets. It goes without saying that other combinations of conversion coefficients may be used.

FIG. 6 is a table showing the selected twelve transform coefficients, which are classified by the stripe direction and the stripe period. The horizontal group (Y_E) includes transform coefficients S ₀₂ , S ₀₃ and S ₀₄ , and includes horizontal stripes as can be seen from the base image shown in FIG. In addition, the horizontal diagonal group (YN
The _E) contains transform coefficients S ₁₂ and S _13, and includes an oblique stripe near the lateral direction as seen from the base image shown in FIG. The conversion coefficient S is assigned to the diagonal group (N_E).
₁₁ and S ₂₂ are included, includes diagonal stripes as can be seen from the base image shown in FIG. In addition, vertical and diagonal groups (T
The n_e) contains transform coefficients S ₂₁ and S _31, and includes an oblique stripe near the vertical direction as seen from the base image shown in FIG. Further, the vertical group (T_e) is included conversion coefficient S _20, S ₃₀ and S _40, and includes a vertical stripe as seen from the base image shown in FIG.

When the fringe period to be detected is larger than the fringe period shown in FIG. 6, the size of the rectangular block MP is set to twice or more, or the size of the rectangular image Should be compressed to 1/2 or more.

The DCT processing unit 22 performs the above-described DCT processing in units of rectangular blocks on all of the 64 × 64 rectangular blocks, that is, all elements of the rectangular block matrix MB, thereby obtaining the 12 types of rectangular blocks shown in FIG. For each of the transform coefficients, it is possible to obtain the spatial distribution of the fringe feature amount represented by the 64 × 64 two-dimensional matrix _MSuv over the entire captured image. MS _uv can be represented by the following equation.

[0056]

(Equation 2)

Returning to the description of the flowchart shown in FIG. Next, the average value / standard deviation calculation unit 23 calculates an average value and a standard deviation of 64 × 64 values in the two-dimensional matrix _MSuv (S3). When no fringes are included in the captured image, the histogram of the values in the two-dimensional matrix _MSuv has a normal distribution in which the frequencies are concentrated near zero. When stripes occur in a part of a minute area in a captured image, the histogram of values in the two-dimensional matrix _MSuv generally has a normal distribution. Since S _uv is a value apart from 0, a peak corresponding to the fringe appears at a position away from the normal distribution.

In order to utilize this statistical principle, the average value / standard deviation calculation unit 23 calculates the average value μ _uv of the normal distribution for each of the 12 types of conversion coefficients shown in FIG.
v) ∈E and standard deviation σ _uv ; (u, v) ∈E are calculated.

Then, the fringe candidate block extracting unit 24 sets a value obtained by multiplying the standard deviation σ _uv by a predetermined constant C _uv ; (u, v) ∈E as a threshold, and calculates a value between the conversion coefficient S _uv and the average value μ _uv. A set of rectangular blocks whose distance is equal to or larger than the threshold is extracted as a stripe candidate block group (S4). FIG. 7 shows an example of extraction of a fringe candidate block group. A rectangular block group 37 in which the distance between the conversion coefficient S _uv and the average value μ _uv is equal to or _larger than a threshold is extracted as a fringe candidate block group. The stripe candidate block group GB _uv is represented by the following equation.

[0060]

(Equation 3)

As a special case, stripes may occur in the entire area or most of the area of the captured image. Therefore, the calculated value of the standard deviation σ _uv is not used as it is.
It is desirable to use the method in combination with a method of directly managing the value and evaluating the whole captured image.

Further, the fringe candidate block extraction unit 24 uses the value obtained by multiplying the standard deviation σ _uv by C _uv as the threshold value, so that the portion where the conversion coefficient value is relatively distant from 0 in the entire captured image, That is, a portion having a relatively high fringe contrast (fringe amplitude) is extracted. This processing eliminates the influence of an absolute change in the fringe contrast due to a change in the illumination intensity during imaging and a change in the light reflectance of the surface of the inspection object, and enables a highly robust inspection.

Returning to the description of the flowchart shown in FIG. Next, the direction-specific filter processing unit 25 _applies a two-dimensional shape characteristic of the stripe to the stripe candidate block group GB _uv corresponding to the twelve types of transform coefficients S _uv extracted by the stripe candidate block extraction unit 24. Filtering takes into account
A region where a stripe having a predetermined characteristic amount is generated is detected (S
5).

Since the two-dimensional shape characteristics of the stripe, particularly the change in the direction of the stripe and the period of the stripe, are smooth in two-dimensional space,
The change in the minute area is negligible. The direction-specific filter processing unit 25 performs filter processing on each of the five direction-specific groups illustrated in FIG. 6 using an operator that takes into account the two-dimensional shape characteristics of the stripes. FIG. 8 shows an example of the shape of the operator, which is a horizontal group mask (Y_MSK) shown in (a), a horizontal diagonal group mask (YN_MSK) shown in (b), and a diagonal group mask shown in (c). (N_MSK), vertical and diagonal group masks (TN_MSK) shown in (d) and (e)
The vertical group mask (T_MSK) shown in FIG. The operator may have a shape other than those shown in FIGS.

For example, the horizontal group Y_E = ｛(u,
v) = 3, corresponding to three transform coefficients S ₀₂ , S ₀₃ and S ₀₄ when performing filter processing on transform coefficients included in (0,2), (0,3), (0,4)} The horizontal stripe candidate block group Y_GB including the stripe candidate block groups GB ₀₂ , GB _03, and GB ₀₄ can be represented by the following equation.

[0066]

(Equation 4)

The extraction of the horizontal stripe candidate block group Y_GB is performed by sequentially scanning the 64 × 64 rectangular block matrix MB, and the above three types of stripe candidate block groups GB ₀₂ , G
This is possible by searching for a rectangular block in which at least one fringe candidate block exists among B ₀₃ and GB ₀₄ . Then, from the horizontal stripe candidate block group Y_GB, the direction-specific filter processing unit 25 removes only blocks in which horizontal stripe candidate blocks are continuously present in the form of a horizontal group mask Y_MSK shown in FIG. Y
By leaving as _WB, an isolated fringe candidate block is removed. If the operation of extracting only the continuous horizontal stripe candidate blocks is defined as an operator f _[ Y_MSK _] ·, the horizontal stripe block group Y_WB can be expressed by the following equation.

[0068]

(Equation 5)

FIG. 9 is a diagram schematically showing the extraction of the horizontal stripe block. By searching for a block in which at least one fringe candidate block exists from among the fringe candidate block groups GB ₀₂ , GB _03, and GB ₀₄ shown in FIGS. 9A to 9C, FIG. The horizontal stripe candidate block group Y_GB shown can be extracted. Then, the direction-specific filter processing unit 25 performs a filtering process on the horizontal stripe candidate block group Y_GB shown in FIG. 9D using the horizontal group mask Y_MSK, and thereby the horizontal stripe block group shown in FIG. Extract Y_WB.

The direction-specific filter processing unit 25 performs the same filter processing on the horizontal and oblique group YN_E and the oblique group N_
E, vertical and diagonal group TN_E, and vertical group T_E
Perform for By obtaining the logical sum of the extracted horizontal and oblique stripe block group YN_WB, the oblique stripe block group N_WB, the vertical and oblique stripe block group TN_WB, the vertical stripe block group T_WB, and the above-described horizontal stripe block group Y_WB, the stripe blocks in all directions are obtained. The omnidirectional fringe block group WB obtained by superimposing the groups is output as a fringe detection area which is the final result. This omnidirectional stripe block group WB can be represented by the following equation.

[0071]

(Equation 6)

The fringe detecting device described above can be realized by causing a computer to execute a fringe detecting program. A method for realizing the fringe detecting device by this computer will be described below, but the fringe detecting device in the present embodiment is not limited to this. For example, the DCT processing that requires the longest time in the program processing can be implemented by hardware to speed up the processing.

FIG. 10 is a diagram showing an example of the appearance of the fringe detecting device of the present invention. The fringe detecting device includes a computer main body 1, a graphic display device 2, a magnetic tape device 3 on which a magnetic tape 4 is mounted, a keyboard 5, a mouse 6, a CD.
-A communication modem 9 including a CD-ROM device 7 to which a ROM (Compact Disc-Read Only Memory) 8 is mounted. The fringe detection program is a magnetic tape 4 or CD-R
It is supplied by a storage medium such as OM8 and executed by the computer main body 1. Further, the fringe detection program may be supplied to the computer main body 1 from another computer via a communication line and a communication modem 9.

FIG. 11 is a block diagram showing an example of the configuration of the fringe detecting device according to the present embodiment. A computer body 1 shown in FIG. 10 includes a CPU 10, a ROM (Read Only Mem
ory) 11, a RAM (Random Access Memory) 12, and a hard disk 13. The CPU 10 includes a graphic display device 2, a magnetic tape device 3, a keyboard 5, a mouse 6, a CD-ROM device 7, a communication modem 9,
The processing is performed while inputting / outputting data to / from the OM 11, the RAM 12, or the hard disk 13. The fringe detection program recorded on the magnetic tape 4 or the CD-ROM 8 is
Magnetic tape device 3 or CD-ROM by CPU 10
The data is temporarily stored in the hard disk 13 via the device 7.
The CPU 10 detects a fringe by appropriately loading a fringe detection program from the hard disk 13 into the RAM 12 and executing the program.

As described above, according to the fringe detecting device of the present embodiment, the captured image is subdivided into rectangular blocks, and the rectangular blocks are subjected to DCT processing to analyze the spatial frequency of the fringes. Therefore, two-dimensional feature analysis including the direction of the stripe can be performed.

Further, since the feature amount of the stripe (direction, period, and amplitude of the stripe) is extracted for each rectangular block, it is possible to detect even a stripe that occurs in a small area of about the size of the rectangular block. Became possible.

Since a rectangular block having a relatively large amplitude value of an image in a two-dimensional matrix is extracted as a stripe candidate block, a change in illumination intensity at the time of imaging and light reflection on the surface of the inspection object are performed. The effect of the change in the fringe contrast due to the change in the rate was eliminated, and highly robust detection became possible.

Further, since the filter processing is performed in consideration of the two-dimensional shape characteristics of the stripes, it is possible to remove the influence of brightness change due to white noise, uneven reflection on the surface of the inspection object, or texture. It became.

(Embodiment 2) The photoconductor drum inspection apparatus according to Embodiment 2 is obtained by applying the fringe detection apparatus according to Embodiment 1 to a thin film on the surface of a photoconductor drum used in a copying machine or the like.

FIG. 12 shows a cross-sectional structure near the surface of the photosensitive drum. The photoconductor drum 40 is made of an aluminum pipe 4
1 and a multilayer thin film 42 which is a photoconductor formed on the surface of the aluminum tube 41. When the surface of the photosensitive drum 40 is irradiated with a light source 43 having a single wavelength of λ, light interference depending on the thickness d of the multilayer thin film 42 occurs. Therefore, when there is a change in the thickness d, interference fringes such as contour lines of a map are observed. If there is a defective portion where the thickness of the multilayer thin film 42 changes abruptly, in a copying machine, shading unevenness corresponding to the defective portion occurs on the copy paper. In this defective portion, the interval between the interference fringes becomes narrow, so that it is possible to detect a defective portion of the photosensitive drum 40 by detecting a portion where the fringe cycle of the interference fringes is short.

FIG. 13 is a block diagram showing a schematic configuration of a photosensitive drum inspection apparatus according to the present embodiment. The photoconductor drum inspection apparatus includes a light source 43 having a single wavelength, and a line sensor 4 for imaging regular reflection light from the photoconductor drum 40.
4 and a rotation drive unit 45 for rotating the photosensitive drum 40
And a rotation control unit 46 for controlling the rotation of the rotation drive unit 45.
, An image memory 47 for storing an image captured by the line sensor 44, and a fringe detection processing unit 48 for performing fringe detection
And

The light source 43 is arranged so that light is applied to the entire area of the photosensitive drum 40 in the longitudinal direction. The line sensor 44 is arranged so as to capture an image of the entire photosensitive drum 40 in the longitudinal direction. The rotation control unit 46 controls the rotation of the rotation drive unit 45 in synchronization with the imaging by the line sensor 44. For example, if the storage capacity of the image memory 47 is 2048 pixels × 2048 pixels, the rotation control unit 46 rotates the image (one frame) of the entire surface of the photosensitive drum 40 so that the image (one frame) fits in the storage capacity of the image memory 47. The controller 45 is controlled to rotate the photosensitive drum 40.

The fringe detection processing unit 48 performs fringe detection processing on the image of one frame stored in the image memory 47. Since the processing procedure is the same as the processing procedure of the fringe detection device in the first embodiment, the details are described in detail. Detailed description will not be repeated.

As described above, according to the photoconductor drum inspection apparatus of the present embodiment, it is possible to automatically detect a defective portion on the surface of the photoconductor drum. Can be obtained also in the inspection of the photosensitive drum.

(Embodiment 3) A liquid crystal panel inspection apparatus according to Embodiment 3 is an application of the fringe detection apparatus according to Embodiment 1 to inspection of gap unevenness between bonded glasses in a liquid crystal panel.

FIG. 14 shows a sectional structure of the liquid crystal panel 49. The liquid crystal panel 49 includes two glasses 50 and a liquid crystal 51 injected into a gap between the two glasses 50.
And When the surface of the liquid crystal panel 49 is irradiated with the light source 53 having a single wavelength of λ, optical interference occurs depending on the value d of the gap between the glasses. Therefore, when there is a change in the value d of the gap between glasses, an interference fringe like a contour line of a map is observed.

In the manufacturing process of the liquid crystal panel, the liquid crystal 51 is injected into the gap between the glasses, so that the gap unevenness of the gap between the glasses affects the product quality.
Therefore, it is possible to detect gap unevenness by extracting a portion where interference fringes occur, and to find out a defect of the liquid crystal panel 49.

FIG. 15 is a block diagram showing a schematic configuration of a liquid crystal panel inspection apparatus according to the present embodiment. The liquid crystal panel inspection apparatus includes a light source 53 having a single wavelength and a line sensor 52 for imaging interference fringes generated on the liquid crystal panel 49.
, An image memory 47 for storing an image captured by the line sensor 52, and a fringe detection processing unit 48 for performing fringe detection
And

The light source 53 is arranged so that light is diffused and radiated over the entire surface of the liquid crystal panel 49. Further, the line sensor 52 is disposed so as to capture an image of the entire area of the liquid crystal panel 49. For example, if the storage capacity of the image memory 47 is 512 pixels × 512 pixels, an image (one frame) of the entire surface of the liquid crystal panel 49 is stored in the image memory 47.
The imaging is performed so as to fit in the storage capacity of.

The fringe detection processing unit 48 performs fringe detection processing on an image for one frame stored in the image memory 47. Since the processing procedure is the same as that of the fringe detecting apparatus in the first embodiment, the details are described in detail. Detailed description will not be repeated.

As described above, according to the liquid crystal panel inspection apparatus of the present embodiment, it is possible to automatically detect a defective portion on the surface of a liquid crystal panel. This effect can be obtained even in the inspection of the liquid crystal panel.

The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a fringe detection device according to a first embodiment of the present invention.

FIG. 2 is a flowchart illustrating a processing procedure of the fringe detection device according to the first embodiment of the present invention.

FIG. 3 is a diagram schematically showing optical fringes appearing on the surface of an inspection object.

FIG. 4 is a diagram showing a state in which a captured image is subdivided into rectangular blocks.

FIG. 5 is a diagram showing a base image corresponding to a transform coefficient _Suv .

FIG. 6 is a table showing twelve selected transform coefficients.

FIG. 7 is a diagram illustrating an example of extraction of a stripe candidate block group.

FIG. 8 is a diagram illustrating an example of the shape of an operator used for the filtering process.

FIG. 9 is a diagram for describing extraction of a horizontal stripe block group.

FIG. 10 is a diagram illustrating an example of an external appearance of a computer that realizes fringe detection according to the first embodiment.

11 is a diagram illustrating a configuration example of a computer illustrated in FIG.

FIG. 12 is a diagram illustrating a cross-sectional structure near a surface of a photoconductor drum.

FIG. 13 is a diagram illustrating a schematic configuration of a photoconductor drum inspection apparatus.

FIG. 14 is a diagram showing a cross-sectional structure of a liquid crystal panel.

FIG. 15 is a diagram showing a schematic configuration of a liquid crystal panel inspection device.

FIG. 16 is a diagram for explaining a problem in the conventional measurement of the fringe period.

[Explanation of symbols]

 Reference Signs List 1 computer main body 2 graphic display device 3 magnetic tape device 4 magnetic tape 5 keyboard 6 mouse 7 CD-ROM device 8 CD-ROM 9 communication modem 10 CPU 11 ROM 12 RAM 13 hard disk 21 rectangular block division unit 22 DCT processing unit 23 average value / Standard deviation calculation unit 24 stripe candidate block extraction unit 25 direction-specific filter processing unit 26 processing result merge unit 40 photoconductor drum 41 aluminum tube 42 multilayer thin film 43,53 light source 44,52 line sensor 45 rotation drive unit 46 rotation control unit 47 image memory 48 fringe detection processing unit 49 liquid crystal panel 50 glass 51 liquid crystal

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G06F 15/70 330F F-term (Reference) 2F065 AA49 AA56 BB02 CC25 DD11 FF06 FF51 GG16 GG18 GG21 JJ02 JJ03 JJ25 JJ26 QQ00 QQ21 QQ24 QQ32 QQ33 QQ42 SS13 2G051 AA73 AA90 AB20 BA20 CA03 CA04 CB01 DA08 EA14 EA20 EB01 EB02 EC02 EC03 EC05 ED01 FA10 5B057 AA03 CG05 CH09 DA03 DB02 DC22 5L096 BA03 CA16 FA26 FA32.

Claims (12)

[Claims] A dividing unit configured to divide a captured image of an optical fringe of an inspection object into blocks each including a plurality of pixel sets; A fringe detection device, comprising: processing means for performing discrete cosine transform; and evaluation means for evaluating the inspection object based on a processing result of the processing means. 2. The evaluation means for generating a two-dimensional matrix for each transform coefficient obtained by the processing means, and extracting a block having a relatively large amplitude in the two-dimensional matrix as a stripe candidate block. The fringe detecting device according to claim 1, further comprising an extracting unit. 3. The calculating means for calculating an average value and a standard deviation for each conversion coefficient with respect to a processing result by the processing means, and calculating the average value and the standard deviation calculated by the calculating means. 3. A fringe detecting apparatus according to claim 2, further comprising: a fringe candidate block extracting means for extracting the fringe candidate block based on the pattern. 4. A fringe candidate block extracting means for extracting, as a fringe candidate block, a block in which a distance between a transform coefficient of the block and the average value is equal to or greater than a value obtained by multiplying the standard deviation by a predetermined value. 4. The fringe detecting device according to claim 3, comprising: 5. The evaluation means further includes a stripe extraction means for extracting blocks in which the stripe feature amounts are similar from among the stripe candidate blocks extracted by the extraction means and the stripe candidate blocks are adjacent to each other. The fringe detection device according to claim 2. 6. The fringe extracting unit includes a filtering unit for performing a filtering process in consideration of directionality on a fringe candidate block for each transform coefficient extracted by the extracting unit. Fringe detector. 7. The fringe detecting device according to claim 6, wherein said fringe detecting device further includes a merging unit for merging a processing result of each transform coefficient by said filter processing unit. 8. The fringe detecting device according to claim 1, wherein said processing means includes means for extracting only a specific transform coefficient from transform coefficients obtained by discrete cosine transform. . 9. A light emitting unit for irradiating the photosensitive drum with light; an imaging unit for imaging optical fringes of the photosensitive drum generated by reflected light of the light from the light emitting unit; Control means for controlling the rotation of the drum; dividing means for dividing the image taken by the image pickup means into blocks composed of a plurality of pixel sets; information in the blocks divided by the dividing means A photosensitive drum inspection apparatus comprising: a processing unit for performing a discrete cosine transform on the photosensitive drum; and an evaluation unit for evaluating the photosensitive drum based on a processing result of the processing unit. 10. A light emitting unit for irradiating light to a liquid crystal panel, an image pickup unit for picking up an optical stripe of the liquid crystal panel generated by reflected light of the light from the light emitting unit, and an image pickup unit for picking up an image. Dividing means for dividing the divided image into blocks composed of a plurality of pixel sets, processing means for performing discrete cosine transform on information in the blocks divided by the dividing means, and the processing means A liquid crystal panel inspection apparatus, comprising: an evaluation unit for evaluating the liquid crystal panel based on a processing result of the liquid crystal panel. 11. A step of dividing a captured image of an optical fringe of an inspection object into blocks each including a plurality of pixel sets, and performing a discrete cosine transform on information in the divided blocks. And a step of evaluating the inspection object based on a processing result of the discrete cosine transform. 12. A step of dividing a captured image of an optical fringe of an inspection object into blocks each including a plurality of pixel sets, and a step of performing discrete cosine transform on information in the divided blocks. And a step of evaluating the inspection object based on a result of the discrete cosine transform.